The invention relates generally to a system for automatic estimation of output mapping parameters and particularly, but not by way of limitation, to methods and apparatus for automatic estimation of MVAT and MVPEAK parameters of rate-adaptive pacing curves.
Many control systems rely on an output mapping to convert a measured control input to a desired control output. The output mapping is a graphical, tabular or other mathematical function of control output versus control input. As an example, a burner system with fuel and oxygen feeds may measure fuel feed rate as a control input and utilize output mapping to define the desired oxygen feed rate as a control output. The output mapping of oxygen feed rate versus fuel feed rate may not be linear, e.g., requiring increasing levels of excess oxygen at higher fuel feed rates to provide efficient burning of the fuel. While theoretical considerations allow designers to calculate an output mapping of the desired control output as a function of the control input, one or more of the parameters in the calculations may be empirical, i.e., based on experience or observations as opposed to theory or conjecture. Testing of the control system may be required to define the empirical parameters for proper operation of the control system. Another example of control systems utilizing output mapping are some cardiac rhythm management systems.
Cardiac rhythm management systems include, among other things, pacemakers, also referred to as pacers. Pacemakers deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart, such as via a transvenous leadwire having one or more electrodes disposed in the heart. Heart contractions are initiated in response to such pace pulses. By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, greatly improving its efficiency as a pump. Pacemakers are often used to treat patients with bradyarrhythmias, that is, hearts that beat too slowly, or irregularly.
There exists a class of pacemakers known as variable rate or rate-adaptive pacemakers which include a physiologic sensor indicative of metabolic demand and a variable rate pulse generator responsive to changes in metabolic demand. Some physiologic sensors for determining metabolic demand include minute ventilation (MV) sensors for measuring trans-thoracic impedance variations and generating an output signal varying as a function of the patient""s minute ventilation, and accelerometers for measuring body vibration during physical activity and generating an output signal varying as a function of the patient""s movement. Accelerometers are typically filtered and processed such that the resulting output signal is indicative of the patient""s exercising activity, and not of external vibration sources or internal noise. Other physiologic sensors are used, e.g., blood pH, blood temperature, QT interval, blood oxygen saturation, respiratory rate and others.
Rate-adaptive pacemakers attempt to pace a patient""s heart at a rate corresponding to the patient""s metabolic demand. They accomplish this by utilizing an output mapping to convert a given physiologic sensor input to a unique output signal level. Although many of the physiologic sensors are highly correlated to metabolic demand, this correlation may be empirical in nature, thus making it difficult to determine the appropriate output mapping prior to implantation of the pacemaker. If the patient""s actual metabolic demand differs from the predetermined output mapping, the paced rate will be either too high or too low. If the paced rate is too high, the patient may feel palpitated or stressed. If too low, the patient may feel fatigued, tired or dizzy.
As will be seen from the above concerns, there exists a need for an improved method of tuning output mapping. The above-mentioned problems with matching pacing to a patient""s metabolic demand and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
One embodiment includes a method of adjusting an output mapping of a control output versus a control input for a control system. The method includes collecting first signal input data from a first sensor indicative of motion of the control system, collecting second signal input data from a second sensor, and storing the first and second signal input data in a memory, thereby producing stored first signal input data and stored second signal input data. The method further includes detecting steady-state motion of the system from the stored first signal input data, calculating at least one parameter for the output mapping in response to changes in the stored second signal input data during a period of steady-state motion, thereby producing at least one calculated parameter, and adjusting the output mapping in response to the at least one calculated parameter. In another embodiment, collecting first signal input data from a first sensor includes collecting first signal input data from an accelerometer. In a further embodiment, detecting steady-state motion of the system includes subjecting the stored first signal input data to Fourier analysis to convert the stored first signal input data to its harmonically-related frequency components.
Another embodiment includes a method of adjusting a rate-adaptive curve of a pacemaker. The method includes collecting first signal input data from a first sensor indicative of motion of the pacemaker, collecting second signal input data from a minute ventilation sensor, and storing the first and second signal input data in a memory, thereby producing stored first signal input data and stored second signal input data. The method further includes detecting steady-state motion of the pacemaker from the stored first signal input data, calculating at least one parameter for the rate-adaptive curve in response to changes in the stored second signal input data during a period of steady-state motion, thereby producing at least one calculated parameter, and adjusting the rate-adaptive curve in response to the at least one calculated parameter. In a further embodiment, collecting first signal input data from a first sensor includes collecting first signal input data from an accelerometer. In a still further embodiment, detecting steady-state motion of the pacemaker includes subjecting the stored first signal input data to Fourier analysis to convert the stored first signal input data to its harmonically-related frequency components. In one embodiment, detecting steady-state motion of the pacemaker includes detecting steady-state motion when the frequency components exhibit an amplitude maxima at a frequency component in the range of about 1 to 4 Hertz.
A further embodiment includes a method of adjusting a two-slope rate-adaptive curve of a pacemaker, wherein the two-slope rate-adaptive curve is defined by parameters including minute ventilation at anaerobic threshold and minute ventilation at peak exercise. The method includes collecting first signal input data from an accelerometer, collecting second signal input data from a minute ventilation sensor, and storing the first and second signal input data in a memory, thereby producing stored first signal input data and stored second signal input data. The method further includes detecting steady-state motion of the pacemaker from the stored first signal input data by subjecting the stored first signal input data to Fourier analysis, calculating the minute ventilation at anaerobic threshold and minute ventilation at peak exercise in response to changes in the stored second signal input data, and adjusting the rate-adaptive curve in response to the calculated minute ventilation at anaerobic threshold and the calculated minute ventilation at peak exercise.
Yet another embodiment includes a control system. The control system includes a processor, a memory coupled to the processor and having output mapping data stored thereon defining an output mapping, and a regulator coupled to the processor. The control system further includes a first sensor input coupled to the processor and adapted to receive first sensor input data indicative of motion of the control system, a second sensor input coupled to the processor and adapted to receive second sensor input data, a control output coupled to the regulator, and a detection module coupled to the processor and adapted to detect steady-state motion of the control system in response to the first sensor input data. The processor is adapted to adjust the output mapping data in response to changes in the second sensor input data when the detection module detects steady-state motion of the control system.
One embodiment includes a rate-adaptive pacemaker. The rate-adaptive pacemaker includes a processor, a memory coupled to the processor and having output mapping data stored thereon defining a rate-adaptive curve, and a variable-rate pulse generator coupled to the processor. The rate-adaptive pacemaker further includes a first sensor input coupled to the processor and adapted to receive first sensor input data indicative of motion of the pacemaker, a second sensor input coupled to the processor and adapted to receive second sensor input data from a minute ventilation sensor, a pulse output coupled to the variable-rate pulse generator, and a detection module coupled to the processor and adapted to detect steady-state motion of the pacemaker in response to the first sensor input data. The processor is adapted to adjust the output mapping data in response to changes in the second sensor input data when the detection module detects steady-state motion of the pacemaker. In another embodiment, the rate-adaptive pacemaker further includes an accelerometer coupled to the first sensor input to provide the first sensor input data.
Another embodiment includes a rate-adaptive pacemaker. The rate-adaptive pacemaker includes a processor, a memory coupled to the processor and having output mapping data stored thereon defining a rate-adaptive curve, and a variable-rate pulse generator coupled to the processor. The rate-adaptive pacemaker further includes a first sensor input coupled to the processor, a second sensor input coupled to the processor, and a pulse output coupled to the variable-rate pulse generator. The memory has instructions stored thereon capable of causing the processor to perform a method. The method includes collecting first signal input data from a first sensor indicative of motion of the pacemaker at the first sensor input, collecting second signal input data from a minute ventilation sensor at the second sensor input, and storing the first and second signal input data in the memory, thereby producing stored first signal input data and stored second signal input data. The method further includes detecting steady-state motion of the pacemaker from the stored first signal input data, calculating at least one parameter for the rate-adaptive curve in response to changes in the stored second signal input data during a period of steady-state motion, thereby producing at least one calculated parameter, and adjusting the output mapping data in response to the at least one calculated parameter. In a further embodiment, collecting first signal input data from a first sensor comprises collecting first signal input data from an accelerometer.
Other embodiments include methods and apparatus of varying scope.